What is the greatest threat to Microsoft's dominance: Google Inc. or open source? The answer is both, especially when they're working together. The search giant is always careful to squelch speculation of any looming clash of the titans. When Google added a presentation app to its online office suite, for example, CEO Eric Schmidt adamantly stated it was not a rival to Microsoft Office. Google's bevy of Ph.D.s came up with the perfect solution: a way to fight Microsoft without appearing to do so. Open source lies at the heart of that strategy.